A continuing concern in the manufacture of galvanic cells is that electrolyte may creep through a sealed interface of the cell and leak out of the cell. Electrolyte leakage may shorten cell life and can also cause a corrosive deposit to form on the exterior surface of the cell which detracts from the cell's appearance and marketability. These corrosive salts may also damage the device in which the cell is housed. Electrolyte leakage occurs in cell systems having aqueous or nonaqueous electrolytes, such as organic solvent-based electrolytes and liquid inorganic cathode-electrolytes for example those based on thionyl chloride and sulfuryl chloride. Electrolytes such as alkaline electrolytes have an affinity for wetting metal surfaces and are known to creep through a sealed interface of a galvanic cell.
Much effort has been expended in the past in trying to achieve a means for reducing such electrolyte leakage in cells. Among the approaches adopted in the prior art is that described in U.S. Pat. application No. 391,421, filed on June 23, 1982. This application relates to a construction of galvanic cells wherein a two-piece cover is employed. At least one aperture is provided through the inner cover, through which electrolyte may be rapidly dispensed and quickly absorbed into a container having cell components therein. Utilizing this cell construction, electrolyte may be added in a manner which effectively prevents the sealing surfaces of the cell from becoming wetted with electrolyte, thus reducing the problem of electrolyte leakage.
A problem involved with such cell construction arises from the fact that the electrode collector tab is welded to the inner surface of the cell's inner or outer cover. This welding step occasionally leads to cell shorting due to cutting of the separator by movement of the tab during the welding procedure and/or during the positioning of the outer cover. In addition, this welding requirement makes automation of the cell manufacture operation difficult.
It is therefore an object of the present invention to provide an improved construction of cells having a two-piece cover, the inner cover of which has at least one aperture therein through which electrolyte may be dispensed into the cell container, which construction will reduce the danger of cell shorting due to tearing of the separator during cell assembly.
It is a further object of this invention to provide a construction of cells having a two-piece cover, the inner cover of which has at least one aperture therein through which electrolyte may be dispensed, which construction is readily adaptable to an automated manufacturing process.
It is a further object of this invention to provide a process for the production of sealed galvanic cells having a two-piece cover construction in which the danger of cell shorting due to tearing of the separator during cell assembly is reduced.
The foregoing and additional objects of this invention will become apparent from the following description and accompanying drawings and examples.